Enlarge/ A Sixgill Hagfish (Eptatretus hexatrema) in False Bay, South Africa.
The humble hagfish is an ugly, gray, eel-like creature best known for its ability to unleash a cloud of sticky slime onto unsuspecting predators, clogging the gills and suffocating said predators. That’s why it’s affectionately known as a “snot snake.” Hagfish also love to burrow into the deep-sea sediment, but scientists have been unable to observe precisely how they do so because the murky sediment obscures the view. Researchers at Chapman University built a special tank with transparent gelatin to overcome this challenge and get a complete picture of the burrowing behavior, according to a new paper published in the Journal of Experimental Biology.
“For a long time we’ve known that hagfish can burrow into soft sediments, but we had no idea how they do it,” said co-author Douglas Fudge, a marine biologist who heads a lab at Chapman devoted to the study of hagfish. “By figuring out how to get hagfish to voluntarily burrow into transparent gelatin, we were able to get the first ever look at this process.”
As previously reported, scientists have been studying hagfish slime for years because it’s such an unusual material. It’s not like mucus, which dries out and hardens over time. Hagfish slime stays slimy, giving it the consistency of half-solidified gelatin. That’s due to long, thread-like fibers in the slime, in addition to the proteins and sugars that make up mucin, the other major component. Those fibers coil up into “skeins” that resemble balls of yarn. When the hagfish lets loose with a shot of slime, the skeins uncoil and combine with the salt water, blowing up more than 10,000 times its original size.
From a materials standpoint, hagfish slime is fascinating stuff that might one day prove useful for biomedical devices, or weaving light-but-strong fabrics for natural Lycra or bulletproof vests, or lubricating industrial drills that tend to clog in deep soil and sediment. In 2016, a group of Swiss researchers studied the unusual fluid properties of hagfish slime, specifically focusing on how those properties provided two distinct advantages: helping the animal defend itself from predators and tying itself in knots to escape from its own slime.
Hagfish slime is a non-Newtonian fluid and is unusual in that it is both shear-thickening and shear-thinning in nature. Most hagfish predators employ suction feeding, which creates a unidirectional shear-thickening flow, the better to clog the gills and suffocate said predators. But if the hagfish needs to get out of its own slime, its body movements create a shear-thinning flow, collapsing the slimy network of cells that makes up the slime.
Fudge has been studying the hagfish and the properties of its slime for years. For instance, way back in 2012, when he was at the University of Guelph, Fudge’s lab successfully harvested hagfish slime, dissolved it in liquid, and then “spun” it into a strong-yet-stretchy thread, much like spinning silk. It’s possible such threads could replace the petroleum-based fibers currently used in safety helmets or Kevlar vests, among other potential applications. And in 2021, his team found that the slime produced by larger hagfish contains much larger cells than slime produced by smaller hagfish—an unusual example of cell size scaling with body size in nature.
A sedimentary solution
This time around, Fudge’s team has turned their attention to hagfish burrowing. In addition to shedding light on hagfish reproductive behavior, the research could also have broader ecological implications. According to the authors, the burrowing is an important factor in sediment turnover, while the burrow ventilation changes the chemistry of the sediment such that it could contain more oxygen. This in turn would alter which organisms are likely to thrive in that sediment. Understanding the burrowing mechanisms could also aid in the design of soft burrowing robots.
Enlarge/ Burrowing sequences for a hagfish digging through transparent gelatin.
D.S. Fudge et al., 2024
But first Fudge’s team had to figure out how to see through the sediment to observe the burrowing behavior. Other scientists studying different animals have relied on transparent substrates like mineral cryolite or hydrogels made of gelatin, the latter of which has been used successfully to observe the burrowing behavior of polychaete worms. Fudge et al. opted for gelatin as a sediment replacement housed in three custom transparent acrylic chambers. Then they filmed the gelatin-burrowing behavior of 25 randomly selected hagfish.
This enabled Fudge et al. to identify two distinct phases of movement that the hagfish used to create their u-shaped burrows. First there is the “thrash” stage, in which the hagfish swims vigorously while moving its head from side to side. This not only serves to propel the hagfish forward, but also helps chop up the gelatin into pieces. This might be how hagfish overcome the challenge of creating an opening in the sediment (or gelatin substrate) through which to move.
Next comes the “wriggle” phase, which seems to be powered by an “internal concertina” common to snakes. It involves the shortening and forceful elongation of the body, as well as exerting lateral forces on the walls to brace and widen the burrow. “A snake using concertina movements will make steady progress through a narrow channel or burrow by alternating waves of elongation and shortening,” the authors wrote, and the loose skin of the hagfish is well suited to such a strategy. The wriggle phase lasts until the burrowing hagfish pops its head out of the substrate. The hagfish took about seven minutes or more on average to complete their burrows.
Naturally there are a few caveats. The walls of the acrylic containers may have affected the burrowing behavior in the lab, or the final shape of the burrows. The authors recommend repeating the experiments using sediments from the natural habitat, implementing X-ray videography of hagfish implanted with radio markers to capture the movements. Body size and substrate type may also influence burrowing behavior. But on the whole, they believe their observations “are an accurate representation of how hagfish are creating and moving within burrows in the wild.”
Enlarge/ A kitty named Clover prepares to play with a robot arm in the Cat Royale “multi-species” science/art installation .
Blast Theory – Stephen Daly
Cats and robots are a winning combination, as evidenced by all those videos of kitties riding on Roombas. And now we have Cat Royale, a “multispecies” live installation in which three cats regularly “played” with a robot over 12 days, carefully monitored by human operators. Created by computer scientists from the University of Nottingham in collaboration with artists from a group called Blast Theory, the installation debuted at the World Science Festival in Brisbane, Australia, last year and is now a touring exhibit. The accompanying YouTube video series recently won a Webby Award, and a paper outlining the insights gleaned from the experience was similarly voted best paper at the recent Computer-Human Conference (CHI’24).
“At first glance, the project is about designing a robot to enrich the lives of a family of cats by playing with them,” said co-author Steve Benford of the University of Nottingham, who led the research, “Under the surface, however, it explores the question of what it takes to trust a robot to look after our loved ones and potentially ourselves.” While cats might love Roombas, not all animal encounters with robots are positive: Guide dogs for the visually impaired can get confused by delivery robots, for example, while the rise of lawn mowing robots can have a negative impact on hedgehogs, per Benford et al.
Blast Theory and the scientists first held a series of exploratory workshops to ensure the installation and robotic design would take into account the welfare of the cats. “Creating a multispecies system—where cats, robots, and humans are all accounted for—takes more than just designing the robot,” said co-author Eike Schneiders of Nottingham’s Mixed Reality Lab about the primary takeaway from the project. “We had to ensure animal well-being at all times, while simultaneously ensuring that the interactive installation engaged the (human) audiences around the world. This involved consideration of many elements, including the design of the enclosure, the robot, and its underlying systems, the various roles of the humans-in-the-loop, and, of course, the selection of the cats.”
Based on those discussions, the team set about building the installation: a bespoke enclosure that would be inhabited by three cats for six hours a day over 12 days. The lucky cats were named Ghostbuster, Clover, and Pumpkin—a parent and two offspring to ensure the cats were familiar with each other and comfortable sharing the enclosure. The enclosure was tricked out to essentially be a “utopia for cats,” per the authors, with perches, walkways, dens, a scratching post, a water fountain, several feeding stations, a ball run, and litter boxes tucked away in secluded corners.
Enlarge/ (l-r) Clover, Pumpkin, and Ghostbuster spent six hours a day for 12 days in the installation.
E. Schneiders et al., 2024
As for the robot, the team chose the Kino Gen3 lite robot arm, and the associated software was trained on over 7,000 videos of cats. A decision engine gave the robot autonomy and proposed activities for specific cats. Then a human operator used an interface control system to instruct the robot to execute the movements. The robotic arm’s two-finger gripper was augmented with custom 3D-printed attachments so that the robot could manipulate various cat toys and accessories.
Each cat/robot interaction was evaluated for a “happiness score” based on the cat’s level of engagement, body language, and so forth. Eight cameras monitored the cat and robot activities, and that footage was subsequently remixed and edited into daily YouTube highlight videos and, eventually, an eight-hour film.
Enlarge/ A Day octopus (Octopus cyanea) named Scarlet parachutes her web over a coral head while Dr. Alex Schnell observes.
National Geographic/Disney/Craig Parry
With Earth Day fast approaching once again, it’s time for another new documentary from National Geographic and Disney+: Secrets of the Octopus. It’s the third in what has become a series, starting with the remarkable 2021 documentary Secrets of the Whales (narrated by Sigourney Weaver) and 2023’s Secrets of the Elephants (Natalie Portman as narrator). James Cameron served as producer on all three.
Secrets of the Octopus is narrated by Paul Rudd. Per the official synopsis:
Octopuses are like aliens on Earth: three hearts, blue blood and the ability to squeeze through a space the size of their eyeballs. But there is so much more to these weird and wonderful animals. Intelligent enough to use tools or transform their bodies to mimic other animals and even communicate with different species, the secrets of the octopus are more extraordinary than we ever imagined.
Each of the three episodes focuses on a specific unique feature of these fascinating creatures: “Shapeshifters,” “Masterminds,” and “Social Networks.” The animals were filmed in their natural habitats over 200 days and all that stunning footage is accompanied by thoughtful commentary by featured scientists. One of those scientists is Dr. Alex Schnell, a native Australian and self described storytelling who has worked at Macquarie University, the University of Cambridge, and the Marine Biological Laboratory, among other institutions. Her research focuses on the intelligence of marine animals, particularly cuttlefish and octopuses.
Ars caught up with Schnell to learn more.
Ars Technica: How did you become interested in studying octopuses?
Alex Schnell: I had this pivotal moment when I was young. I had the luxury of actually growing up on the beaches of Sydney so I would spend a lot of time in the water, in rock pools, looking at all the critters. When I was about five years old, I met my first octopus. It was such a monumental moment that opened up a completely different world for me. That’s the day I decided I wanted to be a marine biologist.
Alex Schnell prepares for a dive on the Great Barrier Reef
National Geographic for Disney/Craig Parry
Alex Schnell SCUBA dives over a coral garden on the Great Barrier Reef, while an Australian research vessel floats on the surface above.
National Geographic for Disney/Craig Parry
A Day octopus perched on corals on the Great Barrier Reef.
National Geographic/Disney/Richard Woodgett
Director and DOP Adam Geiger operates a jib arm with Producer / Camera operator, Rory McGuinness, and Camera Assistant, Woody Spark.
National Geographic for Disney/Annabel Robinson
Woody Spark preparing cameras and underwater housings with cinematographer Rory McGuinness.
National Geographic for Disney/Harriet Spark
Alex Schnell observes a Mimic octopus (Thaumoctopus mimicus) while on a dive with wildlife photographer and local dive guide, Benhur Sarinda
National Geographic for Disney/Craig Parry
A Mimic octopus, with striped skin patterning, stretches out all eight arms across black volcanic sand.
National Geographic for Disney/Craig Parry
A Blue-ringed octopus (Hapalochlaena maculosa) displays bright blue rings, a warning that the venom in her bite is deadly.
National Geographic
Ars Technica: What is the focus of your research?
Alex Schnell: I’m a marine biologist that turned into a comparative psychologist—just a fancy word for studying the different minds of animals. What I’m really interested is how intelligence evolved, where and when. The octopus is the perfect candidate to answer some of these questions because they diverge from our own lineage over 550 million years ago. We share an ancestor that looked like a flat worm. So if the octopus shows glimmers of intelligence that we see in ourselves or in animals that are closely related to us, it reveals a lot about the patterns of evolution and how it evolved throughout the animal kingdom.
When you meet an octopus, you really get the sense that there is another being looking out at you. A few years ago, I worked with a team at London School of Economics to write a report reviewing the evidence of sentience in animals. Does the animal have the capacity to feel emotions? We found really strong evidence in octopuses and it ended up changing UK law. Now under UK law, we have to treat octopuses ethically and with compassion.
Ars Technica: One behavioral aspect the series explores is tool use by octopuses. I was struck by the scene where a little coconut octopus uses her clamshell both for shelter and as a shield. I’ve never seen that before.
Alex Schnell: Neither had I. Before we traveled to Indonesia on that shoot, I had read about that particular defensive tool use by the coconut octopus. This species will often be seen carrying around two halves of a coconut, like a mobile den or an RV home. And they use it as protection because they live in a very barren sandy landscape. So I was really excited to see that behavior unfold.
We got more than we bargained for, because in the clip that you mentioned, our coconut octopus was being threatened by this angry mantis shrimp. They pack a really powerful punch that’s been known to break through aquarium glass. And here we have this defenseless little octopus with no bones or anything. In that moment we witnessed her have this idea. She walked over to the shell and picked it up and dragged it back to her original spot and literally used it like a shield to fend off this angry mantis shrimp. She had imagined herself a shield. I saw her get an idea, she imagined it, and she walked over it and used it. I was so blown away that I was screaming with excitement underwater.
Rory McGuinnes, operating an underwater jib arm to film a colorful coral reef on the Lembeh Strait.
National Geographic for Disney/Adam Geiger
Woody Spark tests the controls for the underwater camera-and-slider system
National Geographic for Disney/Adam Geiger
Local dive guides Reifani and Benhur Sarinda observe a Coconut octopus (Amphioctopus marginatus) sheltering between two clam shells.
National Geographic for Disney/Adam Geiger
Woody Spark uses the underwater camera-and-slider system to film a Coconut octopus sheltering between clam shells.
National Geographic for Disney/Adam Geiger
An 8-foot Giant Pacific octopus (Enteroctopus dofleini) rests on the arms of tech diver and octopus enthusiast, Krystal Janicki, on a dive in the shallow waters off Vancouver Island.
National Geographic for Disney/Maxwel Hohn
A Giant Pacific octopus crawls over the sandy seafloor in shallow waters
National Geographic for Disney/Maxwel Hohn
Dr. C.E. O’Brien observes a resting Island octopus (Octopus insularis) on a dive in Turks and Caicos.
National Geographic for Disney/Adam Geiger
Ars Technica: At one point in the series you celebrate having a “conversation” with an octopus. How do octopuses communicate?
Alex Schnell: Octopuses generally communicate with changes to their skin. They can change the color and the texture of their skin in the blink of an eye, and they can also change their posture. What we’ve found with one particular species is that they have cross-species communication, so they collaboratively hunt with some reef fish. Again, I had only read about this behavior until I had a chance to see it in person.
I had this kind of playful idea while I was down there with a Day octopus named Scarlet, who was allowing me to follow her on a lot of her hunts. Because I was so close to her, I noticed she was missing little crabs here and there. Normally her fish hunting partner will do a head stand to point to where the missed food is. I thought, I wonder what’s going to happen if I just point at it, not expecting anything. To my astonishment, she responded and swum right over and looked where I had pointed.
So that’s what I mean by having a conversation with an octopus. I can’t change color sadly, but it’s as if she was responding to my pointing, my “referential signaling,” which is incredible because this is kind of what we see in humans and chimpanzees: this development of communication before language develops. Here we have this octopus responding to a human pointing.
Ars Technica: Scarlet actually reached out her little tentacle to you on multiple occasions; she seemed to recognize you and accept you.
Alex Schnell: I had had those moments before, the ET moment where you get to meet an octopus, and I’ve spoken to other avid divers and people who have a love for octopuses that have had similar experiences. The really special thing with this relationship that I had with Scarlet is that we were able to develop it over weeks and months. Every time I would return to her, she would appear to recognize me quickly and let me back into her world.
What continues to blow me away is that Scarlet grew to trust me really quickly. She reached out and shook my hand after 30 minutes of me watching her, and she let me swim alongside her as she hunted. This is a creature with no skeleton, no shell, no teeth, no claws to protect itself. And despite that extreme vulnerability, she quickly let her guard down. It’s like she was driven by curiosity and this need to reach out and connect, even with an alien creature like me.
Ars Technica: I was surprised to learn that octopuses have such short lifespans.
Alex Schnell: A lot people ask me if they lived longer, would they take over the world? Maybe. It’s life in the fast lane. They are essentially born as orphans because they don’t have any parents or siblings to guide them. They just drift off. They’re loners for most of their lives and they teach themselves. Everything is driven by this intense curiosity to learn. I think that’s why a lot of people have had these incredible moments with octopuses because even the fear or the vulnerability that they might feel is outweighed by a curiosity to interact.
Alex Schnell on the surface in full SCUBA gear.
National Geographic/Harriet Spark
A Coconut octopus pokes an eye out from between partially buried clam shells. Her powerful suckers hold the two shells together for protection from passing predators.
National Geographic for Disney/Craig Parry
Alex Schnell and Benhur Sarinda observe a Coconut octopus walking across the seafloor with clam shells held underneath her web.
National Geographic for Disney/Craig Parry)
A tiny Coconut octopus reaches out to touch Alex Schnell’s hand.
National Geographic for Disney/Craig Parry
An Algae octopus (Abdopus aculeatus) foraging amongst the algae and seagrass in Bunaken Marine Park.
National Geographic/Annabel Robinson
Alex Schnell observing a Southern keeled octopus (Octopus berrima) on a night dive in Port Phillip Bay
National Geographic
A Dorado octopus mother group with eggs
Schmidt Ocean Institute
Ars Technica: Do you find yourself having to be on guard about anthropomorphizing these amazing creatures a bit too much?
Alex Schnell: I think there’s a fine balance. As a trained comparative psychologist, we are taught to be really careful not to anthropomorphize and attribute human traits onto the animals that we see or that we work with. At the same time, I think that we’ve moved too far into a situation that Frans de Waal called “anthro-denialism.” Traits didn’t just sprout up in the human species. They have an evolutionary history, and while they might not be exactly the same in other animals, there are similarities. So sometimes we need to call it what it is. One of der Waal’s examples was researchers who described chimpanzees kissing as “mouth-to-mouth contact” because they didn’t want to anthropomorphize it. Come on guys, they’re kissing.
We do strive to see human traits in other animals. We watched cartoons growing up, we had pets around us, so it’s really hard not to. Our job is as comparative psychologists is to find really strong evidence for the similarities and the differences between the different minds of the animals that we share our planet with.
Ars Technica: What were some of the highlights for you, filming this documentary series?
Alex Schnell: It was challenging in the sense that when the production team first approached me, I was 38 weeks pregnant. So I went out into the field with a five-month-old baby. I was sleep-deprived, trying to go diving and also be on camera. I had worked on natural history films before, but always on the other side of the camera. So it was a steep learning curve.
But it was such a rewarding experience to be able to have the luxury of time to be out with these animals. I had no project because I was on maternity leave. Sometimes when you’re part of a project, you can get tunnel vision. “I’m going to see this particular behavior and that’s what I’m focusing on.” But I could be completely mindful in the moment with my time with octopuses and get to see how they interact in their natural environment. It opens up this incredible secret world that they have. I was seeing things that, yes, I’d read about some of them, but some I’d never heard of before. I think each episode in this series reveals secrets that will take your breath away.
Ars Technica: What is next for you?
Alex Schnell: I’m working on a project called One World, Many Minds. What this project strives to do is accentuate that, yes, we are one world, but there are many minds that make up our collective existence. I really want to showcase the minds of animals like the octopus or the cuttlefish or a big grouper, and show that we have traits that we can recognize, that we can connect with. That will help remove a barrier of otherness, and highlight our shared vulnerability and interconnectedness with animals.
Secrets of the Octopus premieres on Disney+ and Hulu on April 22, 2024.
Enlarge/ SEM Micrograph of a tardigrade, more commonly known as a “water bear” or “moss piglet.”
Cultura RM Exclusive/Gregory S. Paulson/Getty Images
Since the 1960s, scientists have known that the tiny tardigrade can withstand very intense radiation blasts 1,000 times stronger than what most other animals could endure. According to a new paper published in the journal Current Biology, it’s not that such ionizing radiation doesn’t damage tardigrades’ DNA; rather, the tardigrades are able to rapidly repair any such damage. The findings complement those of a separate study published in January that also explored tardigrades’ response to radiation.
“These animals are mounting an incredible response to radiation, and that seems to be a secret to their extreme survival abilities,” said co-author Courtney Clark-Hachtel, who was a postdoc in Bob Goldstein’s lab at the University of North Carolina at Chapel Hill, which has been conducting research into tardigrades for 25 years. “What we are learning about how tardigrades overcome radiation stress can lead to new ideas about how we might try to protect other animals and microorganisms from damaging radiation.”
As reported previously, tardigrades are micro-animals that can survive in the harshest conditions: extreme pressure, extreme temperature, radiation, dehydration, starvation—even exposure to the vacuum of outer space. The creatures were first described by German zoologist Johann Goeze in 1773. They were dubbed tardigrada (“slow steppers” or “slow walkers”) four years later by Lazzaro Spallanzani, an Italian biologist. That’s because tardigrades tend to lumber along like a bear. Since they can survive almost anywhere, they can be found in lots of places: deep-sea trenches, salt and freshwater sediments, tropical rain forests, the Antarctic, mud volcanoes, sand dunes, beaches, and lichen and moss. (Another name for them is “moss piglets.”)
When their moist habitat dries up, however, tardigrades go into a state known as “tun”—a kind of suspended animation, which the animals can remain in for as long as 10 years. When water begins to flow again, water bears absorb it to rehydrate and return to life. They’re not technically members of the extremophile class of organisms since they don’t so much thrive in extreme conditions as endure; technically, they belong to the class of extremotolerant organisms. But their hardiness makes tardigrades a favorite research subject for scientists.
For instance, a 2017 study demonstrated that tardigrades use a special kind of disordered protein to literally suspend their cells in a glass-like matrix that prevents damage. The researchers dubbed this a “tardigrade-specific intrinsically disordered protein” (TDP). In other words, the cells become vitrified. The more TDP genes a tardigrade species has, the more quickly and efficiently it goes into the tun state.
In 2021, another team of Japanese scientists called this “vitrification” hypothesis into question, citing experimental data suggesting that the 2017 findings could be attributed to water retention of the proteins. The following year, researchers at the University of Tokyo identified the mechanism to explain how tardigrades can survive extreme dehydration: cytoplasmic-abundant heat soluble (CAHS) proteins that form a protective gel-like network of filaments to protect dried-out cells. When the tardigrade rehydrates, the filaments gradually recede, ensuring that the cell isn’t stressed or damaged as it regains water.
When it comes to withstanding ionizing radiation, a 2016 study identified a DNA damage suppressor protein dubbed “Dsup” that seemed to shield tardigrade genes implanted into human cells from radiation damage. However, according to Clark-Hatchel et al., it still wasn’t clear whether this kind of protective mechanism was sufficient to fully account for tardigrades’ ability to withstand extreme radiation. Other species of tardigrade seem to lack Dsup proteins, yet still have the same high radiation tolerance, which suggests there could be other factors at play.
A team of French researchers at the French National Museum of Natural History in Paris ran a series of experiments in which they zapped water bear specimens with powerful gamma rays that would be lethal to humans. They published their results earlier this year in the journal eLife. The French team found that gamma rays did actually damage the tardigrade DNA, much like they would damage human cells. Since the tardigrades survived, this suggested the tardigrades were able to quickly repair the damaged DNA.
Further experiments with three different species (including one that lacks Dsup proteins) revealed the tardigrades were producing very high amounts of DNA repair proteins. They also found a similar uptick of proteins unique to tardigrades, most notably tardigrade DNA damage response protein 1 (TDR1), which seems to protect DNA from radiation. “We found that TDR1 protein interacts with DNA and forms aggregates at high concentration suggesting it may condensate DNA and act by preserving chromosome organization until DNA repair is accomplished,” the authors wrote.
Clark-Hatchel et al. independently arrived at similar conclusions from their own experiments. Taken together, the two studies confirm that this extremely rapid up-regulation of many DNA repair genes in response to exposure to ionizing radiation should be sufficient to explain the creatures’ impressive resistance to that radiation. It’s possible that there is a “synergy between protective and repair mechanisms” when it comes to tardigrade tolerance of ionizing radiation.
That said, “Why tardigrades have evolved a strong IR tolerance is enigmatic given that it is unlikely that tardigrades were exposed to high doses of ionizing radiation in their evolutionary history,” Clark-Hatchel et al. wrote. They thought there could be a link to the mechanisms that enable tardigrades to survive extreme dehydration, which can also result in damaged DNA. Revisiting data from desiccation experiments did not show nearly as strong an increase in DNA repair transcripts, but the authors suggest that the uptick could occur later in the process, upon rehydration—an intriguing topic for future research.
Enlarge/ Clown anemonefish (Amphiprion ocellaris) seem to recognize different species of clownfish by counting white stripes.
Kina Hayashi
Many people tend to think of clownfish, with their distinctive white bars against an orange, red, or black background, as a friendly sort of fish, perhaps influenced to some extent by the popular Pixar film Finding Nemo. But clownfish can be quite territorial when it comes to defending their host anemone from intrusion by others, particularly those from their own species. A new paper published in the Journal of Experimental Biology describes how clownfish determine if a fish approaching their home is friend or foe by “counting” the number of white bars or stripes on their bodies.
As previously reported, mathematical ability is often considered uniquely human, but in fact, scientists have found that many animal species—including lions, chimpanzees, birds, bees, ants, and fish—seem to possess at least a rudimentary counting ability or number sense. Crows can understand the concept of zero. So can bees, which can also add and subtract, as can both stingrays and cichlids—at least for a small number of objects (in the range of one to five). Some ants count their steps.
This so-called “numerosity” simply refers to the number of things in a set, according to cognitive psychologist Brian Butterworth, an emeritus professor at University College London and author of Can Fish Count? What Animals Reveal About Our Uniquely Mathematical Minds. It has nothing to do with reasoning or logical mathematical intelligence. This is information that will be in the environment, and counting animals must have some mechanism for extracting this numerical information from the environment. But it nonetheless makes for a fascinating field of study.
In 2022, Kina Hayashi of the Okinawa Institute of Science and Technology (OIST) and several colleagues found that clownfish display more aggressive behavior (e.g., chasing or biting) toward fish (or fish toys) with vertical bar patterns compared with fish with horizontal stripe patterns and that this aggressive behavior lasted longer when directed at fish with vertical bars versus horizontal bars. This behavior appears to influence the position of fish species between host anemones and coral reefs: No fish with vertical bars sought shelter in host anemones, while several species with vertical bars were found in the surrounding coral reefs. But it wasn’t clear how the fish recognized the color patterns or what basic rules controlled this signaling. The study results suggested that it wasn’t based on the mere presence of white bars or how much white color was present on a given fish’s body.
Enlarge/ The plastic models used to measure the clown anemonefish’s aggressive behavior.
This new study builds on that earlier work. This time around, Kayashi and co-authors raised a school of young common clownfish (A. ocellaris) from eggs to ensure that the fish had never set eyes on other species of anemonefish. At six months old, the fish were introduced to several other clownfish species, including Clarke’s anemonefish (A. clarkii), orange skunk clownfish (A. sandaracinos), and saddleback clownfish (A. polymnus).
The researchers placed different species of clownfish, with different numbers of white bars, in small cases inside a tank with a clownfish colony and filmed their reaction. Because they were in a controlled tank environment, there was no chasing or biting. Rather, aggressive behavior was defined as staring aggressively at the other fish and circling the case in which the other fish were held.
They followed up with a second set of experiments in which they presented a colony of clownfish with different plastic models painted with accurate clownfish coloration, with differing numbers of white stripes. The researchers also filmed and measured the degree of aggressive behavior directed at the different plastic models.
Clownfish showing aggression toward another fish with similar stripes. Credit: Kina Hayashi
The results: “The frequency and duration of aggressive behaviors in clown anemonefish was highest toward fish with three bars like themselves,” said Hayashi, “while they were lower with fish with one or two bars, and lowest toward those without vertical bars, which suggests that they are able to count the number of bars in order to recognize the species of the intruder.”
Hayashi et al. cautioned that one limitation of their study is that all the fish used in the experiments were hatched and raised in an environment where they had only encountered other fish of their own species. So, they could not conclusively determine whether the observed behavior was innate or learned. Other species of clownfish also use the same anemone species as hosts, so aggressive behavior toward those species might be more frequent in the wild than observed in the laboratory tank environment.
Enlarge/ These are the kinds of shark teeth discovered in burial sites and other ceremonial remains of the inland Maya communities. From left to right, there’s a fossilized megalodon tooth, great white shark tooth, and bull shark tooth.
Antiquity
The megalodon, a giant shark that went extinct some 3.6 million years ago, is famous for its utterly enormous jaws and correspondingly huge teeth. Recent studies have proposed that the megalodon was robust species of shark akin to today’s great white sharks, only three times longer. And just like the great white shark inspired Jaws, the megalodon has also inspired a 1997 novel and a blockbuster film (2018’s The Meg)—not to mention a controversial bit of “docu-fiction” on the Discovery Channel. But now a team of 26 shark experts are challenging the great white shark comparison, arguing that the super-sized creature’s body was more slender and possibly even longer than researchers previously thought in a new paper published in the journal Paleontologia Electronica.
“Our study suggests that the modern great white shark may not necessarily serve as a good modern analogue for assessing at least certain aspects of its biology, including its size,” co-author Kenshu Shimada, a palaeobiologist at DePaul University in Chicago, told The Guardian. “The reality is that we need the discovery of at least one complete megalodon skeleton to be more confident about its true size as well its body form.” Thus far, nobody has found a complete specimen, only fossilized teeth and vertebrae.
As previously reported, the largest shark alive today, reaching up to 20 meters long, is the whale shark, a sedate filter feeder. As recently as 4 million years ago, however, sharks of that scale likely included the fast-moving predator megalodon (formally Otodus megalodon). Due to incomplete fossil data, we’re not entirely sure how large megalodons were and can only make inferences based on some of their living relatives, like the great white and mako sharks.
Thanks to research published last year on its fossilized teeth, we’re now fairly confident that it shared something else with these relatives: it wasn’t entirely cold-blooded and apparently kept its body temperature above that of the surrounding ocean. Most sharks, like most fish, are ectothermic, meaning that their body temperatures match those of the surrounding water. But a handful of species, part of a group termed mackerel sharks, are endothermic: They have a specialized pattern of blood circulation that helps retain some of the heat their muscles produce. This enables them to keep some body parts at a higher temperature than their surroundings. A species called the salmon shark can maintain a body temperature that’s 20° C warmer than the sub-Arctic waters that it occupies.
Megalodon is also a mackerel shark, and some scientists have suggested that it, too, must have been at least partially endothermic to have maintained its growth rates in the varied environments that it inhabited. The 2023 study measured isotope clumping—which can provide an estimate of the temperature at which a material formed—in mastodon teeth. They confirmed that the megalodon samples were consistently warmer, with an average temperature difference of about 7° C compared to cold-blooded samples.
Enlarge / Who doesn’t thrill to the sight of a microscopic cross-section of a beetle’s rectum? You’re welcome.
Kenneth Veland Halberg
There’s rarely time to write about every cool science-y story that comes our way. So this year, we’re once again running a special Twelve Days of Christmas series of posts, highlighting one science story that fell through the cracks in 2023, each day from December 25 through January 5. Today: red flour beetles can use their butts to suck water from the air, helping them survive in extremely dry environments. Scientists are honing in on the molecular mechanisms behind this unique ability.
The humble red flour beetle (Tribolium castaneum) is a common pantry pest feeding on stored grains, flour, cereals, pasta, biscuits, beans, and nuts. It’s a remarkably hardy creature, capable of surviving in harsh arid environments due to its unique ability to extract fluid not just from grains and other food sources, but also from the air. It does this by opening its rectum when the humidity of the atmosphere is relatively high, absorbing moisture through that opening and converting it into fluid that is then used to hydrate the rest of the body.
Scientists have known about this ability for more than a century, but biologists are finally starting to get to the bottom (ahem) of the underlying molecular mechanisms, according to a March paper published in the Proceedings of the National Academies of Science. This will inform future research on how to interrupt this hydration process to better keep red flour beetle populations in check, since they are highly resistant to pesticides. They can also withstand even higher levels of radiation than the cockroach.
There are about 400,000 known species of beetle roaming the planet although scientists believe there could be well over a million. Each year, as much as 20 percent of the world’s grain stores are contaminated by red flour beetles, grain weevils, Colorado potato beetles, and confused flour beetles, particularly in developing countries. Red flour beetles in particular are a popular model organism for scientific research on development and functional genomics. The entire genome was sequenced in 2008, and the beetle shares between 10,000 and 15,000 genes with the fruit fly (Drosophila), another workhorse of genetics research. But the beetle’s development cycle more closely resembles that of other insects by comparison.
Enlarge/ Food security in developing nations is particularly affected by animal species like the red flour beetle which has specialized in surviving in extremely dry environments, granaries included, for thousands of years.
Kenneth Halberg
The rectums of most mammals and insects absorb any remaining nutrients and water from the body’s waste products prior to defecation. But the red flour beetle’s rectum is a model of ultra-efficiency in that regard. The beetle can generate extremely high salt concentrations in its kidneys, enabling it to extract all the water from its own feces and recycle that moisture back into its body.
“A beetle can go through an entire life cycle without drinking liquid water,” said co-author Kenneth Veland Halberg, a biologist at the University of Copenhagen. “This is because of their modified rectum and closely applied kidneys, which together make a multi-organ system that is highly specialized in extracting water from the food that they eat and from the air around them. In fact, it happens so effectively that the stool samples we have examined were completely dry and without any trace of water.” The entire rectal structure is encased in a perinephric membrane.
Halberg et al. took took scanning electron microscopy images of the beetle’s rectal structure. They also took tissue samples and extracted RNA from lab-grown red flour beetles, then used a new resource called BeetleAtlas for their gene expression analysis, hunting for any relevant genes.
One particular gene was expressed sixty times more in the rectum than any other. Halberg and his team eventually honed in a group of secondary cells between the beetle’s kidneys and circulatory system called leptophragmata. This finding supports prior studies that suggested these cells might be relevant since they are the only cells that interrupt the perinephric membrane, thereby enabling critical transport of potassium chloride. Translation: the cells pump salts into the kidneys to better harvest moisture from its feces or from the air.
Enlarge/ Model of the beetle’s inside and how it extracts water from the air.
Kenneth Halberg
The next step is to build on these new insights to figure out how to interrupt the beetle’s unique hydration process at the molecular level, perhaps by designing molecules that can do so. Those molecules could then be incorporated into more eco-friendly pesticides that target the red flour beetle and similar pests while not harming more beneficial insects like bees.
“Now we understand exactly which genes, cells and molecules are at play in the beetle when it absorbs water in its rectum. This means that we suddenly have a grip on how to disrupt these very efficient processes by, for example, developing insecticides that target this function and in doing so, kill the beetle,” said Halberg. “There is twenty times as much insect biomass on Earth than that of humans. They play key roles in most food webs and have a huge impact on virtually all ecosystems and on human health. So, we need to understand them better.”
Enlarge/ Look at this very good boy taking a test to determine the origin of his spatial bias for a study on how dogs think.
Eniko Kubinyi
Research has shown that if you point at an object, a dog will interpret the gesture as a directional cue, unlike a human toddler, who will more likely focus on the object itself. It’s called spatial bias, and a recent paper published in the journal Ethology offers potential explanations for why dogs interpret the gesture the way that they do. According to researchers at Eötvös Loránd University in Hungary, the phenomenon arises from a combination of how dogs see (visual acuity) and how they think, with “smarter” dog breeds prioritizing an object’s appearance as much as its location. This suggests the smarter dogs’ information processing is more similar to humans.
The authors wanted to investigate whether spatial bias in dogs is sensory or cognitive, or a combination of the two. “Very early on, children interpret the gesture as pointing to the object, while dogs take the pointing as a directional cue,” said co-author Ivaylo Iotchev. “In other words, regardless of the intention of the person giving the cue, the meaning for children and dogs is different. This phenomenon has previously been observed in dogs using a variety of behavioral tests, ranging from simple associative learning to imitation, but it had never been studied per se.”
Their experimental sample consisted of dogs used in a previous 2018 study plus dogs participating specifically in the new study, for a total of 82 dogs. The dominant breeds were border collies (19), vizslas (17), and whippets (6). Each animal was brought into a small empty room with their owner and one of the experimenters present. The experimenter stood 3 meters away from the dog and owner. There was a training period using different plastic plates to teach the dogs to associate either the presence or absence of an object, or its spatial location, with the presence or absence of food. Then they tested the dogs on a series of tasks.
Enlarge/ An object feature conditioning test involving a white round plate and a black square plate.
I.B. Iotchev et al., 2023
For instance, one task required dogs to participate in a maximum of 50 trials to teach them to learn a location of a treat that was always either on the left or right plate. For another task, the experimenter placed a white round plate and a black square plate in the middle of the room. The dogs were exposed to each semi-randomly but only received food in one type of plate. Learning was determined by how quickly each dog ran to the correct plate.
Once the dogs learned those first two tasks, they were given another more complicated task in which either the direction or the object was reversed: if the treat had previously been placed on the right, now it would be found on the left, and if it had previously been placed on a white round plate, it would now be found on the black square one. The researchers found that dogs learned faster when they had to choose the direction, i.e., whether the treat was located on the left or the right. It was harder for the dogs to learn whether a treat would be found on a black square plate or a white round plate.
Enlarge/ The shorter a dog’s head, the higher the “cephalic index” (CI).
I.B. Iotchev et al., 2023
Next the team needed to determine differences between the visual and cognitive abilities of the dogs in order to learn whether the spatial bias was sensory or cognitively based, or both. Selective breeding of dogs has produced breeds with different visual capacities, so another aspect of the study involved measuring the length of a dog’s head, which prior research has shown is correlated with visual acuity. The metric used to measure canine heads is known as the “cephalic index” (CI), defined as the ratio of the head’s maximum width multiplied by 100, then divided by the head’s maximum length.
The shorter a dog’s head, the more similar their visual acuity is to human vision. That’s because there is a higher concentration of retinal ganglion cells in the center of their field of vision, making vision sharper and giving such dogs binocular depth vision. The testing showed dogs with better visual acuity, and who also scored higher on the series of cognitive tests, also exhibited less spatial bias. This suggests that canine spatial bias is not simply a sensory matter but is also influenced by how they think. “Smarter” dogs have less spatial bias.
As always, there are a few caveats. Most notably, the authors acknowledge that their sample consisted exclusively of dogs from Hungary kept as pets, and thus their results might not generalize to stray dogs, for example, or dogs from other geographical regions and cultures. Still, “we tested their memory, attention skills, and perseverance,” said co-author Eniko Kubinyi. “We found that dogs with better cognitive performance in the more difficult spatial bias task linked information to objects as easily as to places. We also see that as children develop, spatial bias decreases with increasing intelligence.”
